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Monday, September 26, 2011

2011’s Off the Charts Weather and Climate Stats

Climate Central: This year is shaping up to be one of the most extreme — if not the most extreme — years in the United States since instrument records began in the late 19th century. Consider a few statistics from just this past June through August to get a better picture of what's been taking place.

Keep in mind that many studies show that certain types of extreme events, such as heavy rainfall events and heat waves, are already becoming more frequent and intense as the climate warms in response to human emissions of greenhouse gases. However, none of these events listed below have been the subject of detailed climate change attribution studies yet, since those take several months to complete, so it would be premature to speculate how big of a role climate change played in their development and evolution.

Map showing the number of days with temperatures above 100 degrees F during summer 2011. Credit: NOAA/NCDC.

This summer was the second-warmest on record in the United States, and the eighth-warmest globally.

Of the Lower-48 states, Texas, Oklahoma, New Mexico, and Louisiana had their hottest summers on record. Two states — Texas and Oklahoma — had average temperatures that were so high, they broke all-time summer heat records for any state in the country. In Texas, the average statewide temperature for the summer was a whopping 86.8°F. Both Texas and Oklahoma eclipsed a benchmark set during the Dust Bowl, when a multiyear drought and a series of withering heat waves transformed the Central states into an arid landscape, driving a mass migration westward.

During the summer of 2011, every state in the Lower-48 except North Dakota and Vermont experienced at least one day with a temperature exceeding 100°F.

As of today, nearly 88 percent of Texas is locked in the grips of "exceptional drought" conditions, which is the most severe category on the U.S. Drought Monitor. In order to climb out of the deep rainfall deficit, parts of Texas and Oklahoma would need nearly two feet of rainfall, yet new climate outlooks for the next several months show drier than average conditions are likely to continue through the winter.

According to Texas State Climatologist John Nielsen-Gammon, it is likely that Texas will soon break a record for the driest 12-month period on record, unless there is widespread heavy rain during the second half of September. He said the drought has cost Texas $5.2 billion in agricultural losses alone, with at least another billion from drought-related wildfires, and the NCDC says this is already Texas' most costly drought in recorded history.

While climate research shows that droughts are likely to occur more frequently and be more severe in a warming world, it's not clear that the Texas drought is directly related to climate change. In fact, a natural climate cycle known as La Niña is the primary suspect for instigating the drought conditions, and its recent return is signaling the continuation of the drought.

What is of concern, though, is that climate change is bound to make droughts like this more severe than they otherwise would be, pushing temperatures higher and thereby drying out the soil even more. Are these summers' temperatures already higher because of climate change? Again, it is too early to say with certainty, but experts on the ground there are suspecting it is the case: As Nelsen-Gammon stated today, "Temperatures are higher than one would expect just from the lack of precipitation."

In a blog post, Nelsen-Gammon estimated how much of the record heat this summer was from man made global warming, and how much from the dry conditions that would have occurred regardless of climate change. Here is what he found: "Compared to long-term averages of summer temperature, the rainfall deficit accounted for about 4°F of excess heat and global warming accounted for about 1°F of excess heat. Warmer temperatures lead to greater water demand, faster evaporation, and greater drying-out of potential fuels for fire. Thus, the impacts of the drought were enhanced by global warming, much of which has been caused by man."

Texas has already experienced its worst wildfire season on record, with the potential for additional "catastrophic fires" in the fall and winter as cold fronts and low pressure systems push through the state, according to Nielsen-Gammon.

According to NCDC, a 429-year tree-ring record of Texas climate conditions shows the summer 2011 drought is equalled by just one other summer, which occurred in 1789.

View of Texas soil moisture conditions in September 2010, showing a small area of dry conditions in eastern Texas. Credit: Texas Office of the State Climatologist. View of Texas soil moisture conditions in March 2011. Credit: Texas Office of the State Climatologist. View of Texas soil moisture conditions in September 2011, showing the widespread extremely dry conditions. Credit: Texas Office of the State Climatologist.

The normally staid monthly climate summary from NCDC contains the following description of the situation in Texas at the end of August: "Ranchers practically liquidated their herds as the water wells went dry and supplemental feeding became too expensive. Likewise, farmers were forced to give up on particular plots and only irrigate what they believed could yield a substantial crop. Across the state, the outlook was extremely bleak."

Here are a series of maps showing how quickly the drought has spread and gotten worse throughout Texas during the past year.

All this heat boosted electricity demand to record levels, the NCDC found. According to NOAA's Residential Energy Demand Temperature Index, the contiguous U.S. temperature-related energy demand was 22.3 percent above average during summer, which was the largest it has been since such records began in 1895.

2011 has had a greater number of billion dollar natural disasters — 10 — than any other year on record.

According to NCDC, the U.S. Climate Extremes Index, which incorporates climate extremes in temperature, rainfall, dry streaks, drought, and tropical cyclones, shows that an area nearly four times the average was affected by extreme climate conditions this summer. This is the third largest summer value of the record, which dates to 1910, the NCDC stated in its monthly climate summary report.

Of course, there was also plenty of heavy rainfall and destructive flooding during the summer, with record flooding from Hurricane Irene and Tropical Storm Lee causing more than a billion dollars in damage in the Mid-Atlantic and Northeast. New York City and Philadelphia broke their all-time monthly rainfall records in August, and New York's John F. Kennedy International Airport recorded its wettest day in history even before either of those storms moved into the Big Apple.

Even if the rest of the year is quiet weather-wise, so many records have already fallen that they ensure 2011's place in history among the top tier of extreme weather years in the US. And if climate change projections come to fruition, this may be the first of many more to come.

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